The present invention relates generally to an implantable multi-lumen multi-conductor lead for use with an implantable medical device.
Permanently implantable electrical lead systems are used in conjunction with implantable medical devices, such as pacemakers and defibrillators. In these applications the lead is used to transmit electrical signals to and/or from the medical device. Leads of this type may be chronically implanted and are expected to exhibit a long service life in a hostile environment of the human body. Cardiac stimulation leads are usually implanted via the cardiovascular venous system such that the distal end of the lead is positioned at an appropriate site within or on top of the surface of the heart.
The traditional lead includes a lead body having a generally circular exterior cross-section and one or more circular lumens, which may be arranged coaxially or parallel to one another. Typically, spiral wound metallic conductors are positioned within one or more lumens of the lead body. The spiral wound conductor also forms a lumen which can receive a stylet to help stiffening the lead as an aid to lead placement during lead implantation.
Alternative conductor designs have been proposed in the context of implantable multiple lumen multiple conductor leads. U.S. Pat. No. 4,608,986 issued to Beranek discloses a round lead having an array of round lumens. This lead places a single xe2x80x9cstraightxe2x80x9d strand of metallic conductor loosely into each lumen. An exotic metal formulation is stated to avoid the problems of breakage due to flexing normally associated with straight conductors.
Current implantable cardiac leads (those cardiac leads implanted for more than 30 days) generally utilize either a type of silicone rubber or a type of polyurethane as the lead""s primary insulation material. However, the lead""s insulationxe2x80x94especially silicone rubber (though it has good biostability)xe2x80x94is not very strong, has a low tear strength, can abrade very easily, and can cold-flow due to cyclic compressive forces or crushing forces applied to the insulation. Common mechanisms that can result in the insulation thinning and finally breaching to failure, are the effect of cyclic compressive forces or crushing forces on the lead""s insulation either from the outside (as in the case of tight sutures on the lead""s suture sleeve, forces from the well-known rib/clavicle crush mechanism) or due, simply, to forces from severe bends of the lead body resulting from the implant itself. Another mechanism which can result in the insulation walls thinning because of abrasion or cold flowing occurs when conductors become kinked or bent, so as to impart a compressive force or abrasive action to the inside of the conductor lumen""s insulation walls. Such insulation wall thinning due to abrasion and/or cold-flow is especially a concern for leads which are multi-lumen/multi-conductor in design.
Other known designs in which conductors are loosely received in oversized lumina which are sometimes being other than circular in cross section are disclosed, variously, in a number of instances, for example, in U.S. Pat. No. 5,303,704 to Molacek et al.; in U.S. Pat. No. 5,324,321 to Pohndorf et al.; in U.S. Pat. No. 5,476,497 to Mower et al.; and to U.S. Pat. No. 5,957,970 to Shoberg et al.
Also, the invention can be distinguished from the construction found in U.S. Pat. No. 5,584,873 to Shoberg et al., which teaches the use of an empty lumen incremental to the conductor carrying lumen that are used to absorb and/or disperse such compressive or crushing forces.
It was in light of the foregoing that the present invention was conceived and has now been reduced to practice.
The present invention relates to implantable transvenous or epimyocardial leads intended for use with a cardiac stimulation device. It includes an elongated lead body of flexible resilient material, for example, silicone rubber or polyurethane, having a longitudinally extending lumen defined by a plurality of longitudinally extending side wall surfaces, adjacent pairs of the side wall surfaces lying in angularly disposed planes and intersecting at an energy absorbing corner ridge. An electrical conductor is located loosely within and extends longitudinally along the lumen between proximal and distal ends. With this construction, forces imposed laterally on the lead body by the conductor engaging the side wall surfaces of the lumen upon bending of the lead body are absorbed without damaging the lead body by reason of engagement of the conductor with a corner ridge causing the corner ridge thereby engaged to recede toward a condition of being coplanar with its subtended pair of side wall surfaces.
This invention employs the use of various shapes of conductor lumina within the insulation of the lead to eliminate or minimize the potential for crushing or compressive forces from either outside the lead body or from the conductor or conductors within the lead body. Such a situation can cause an abrasive and/or a cold flow effect on the lead""s insulation walls of the lead surrounding each conductor. Conventional round lumen walls are not able to disperse or absorb the compressive and/or abrasive forces that can develop, and the insulation of such a lead can therefore become thinned to the point where ultimate failure of the walls of the insulation can occur. Stated another way, conventional, round conductor carrying lumina cannot prevent or mitigate the compressive or crushing forces from causing the conductor to press against (i.e. cyclic compression) or abrade against the insulation""s lumen walls. However, a lumen, which has a shape, that allows for the absorption and/or dispersion of such compressive or crushing forces can reduce, minimize, or even prevent the abrasion or cold flow from occurring to the insulation""s lumen walls.
A primary feature of the invention, then, is the provision of an insulation conductor lumen design for use in cardiac leads which allows for the absorption or dispersion of applied forces to the lead and the lead""s conductors which, in its absence, can cause the conductors to abrade or cause cold flow to the insulation""s lumen walls. Use of the shaped lumen disclosed herein can minimize or even prevent such abrasion and/or cold flow of the insulation.
More specifically, the invention relates to a cardiac bipolar or multi-polar lead in which the primary insulation tubing is silicone rubber, polyurethane or any other suitable material which has at least two or more conductor-carrying-lumen within the lead body, which have a cross-sectional lumen shape that is not round, but is of any shape which can disperse and/or absorb stresses created by external compressive, bending, and/or crushing forces; or stresses created by internal compressive, bending, and/or crushing forces due to the presence of each conductor within the conductor carrying lumen or due to other internal structures and forces.